Passive routing is the most basic form of connectivity provided with Unity. It allows a client session to connect to a single specified Teradata system. Requests are then sent to that system. Optionally, the routing rule can also define a set of failover servers, so that if the first system is not available, the session reconnects to the next available system in the set.
- Volatile tables are only created on one system.
- Queries that access the tables are sent only to the system.
- With only one set of data generated (on a single system), it does not matter if the data generated is deterministic across multiple systems.
- Requests from passive routing rules are never recorded in the recovery log, never affect the Unity data dictionary, or update the unitymgmt transaction table, processing time.
There are five types of passive routing rules.
|Single-System||Specifies only a single system
If that system is not available, the clients using this routing rule cannot connect. Use this option for business users that do not require any failover capability or for Database Administrators that need to connect to a specific system to perform maintenance.
|Preferred||Specifies that the first system in the routing list is the preferred system
It is used if available. If it is not available, the session connects to the next available system in the routing rule system list.
|Least-Used||Allows the client to connect to a set of two or more Teradata systems
When the client connects, it is sent to the system that currently has the least number of passive connections. Use this option to makes sure the systems are evenly balanced when the sessions are running different loads.
|Round Robin||Allows the client to connect to a set of two or more Teradata systems
When the client connects, it is sent to the first system. The next session is sent to the second system, and so on. Use this option when each session is expected to execute the same amount of work.
|Weighted Round Robin||Allows the client to connect to a set of two or more Teradata systems, but in a weighted ratio specified by the routing rule
Use this option when working with systems that are sized differently and can support a different number of connected sessions.